Based on the NIAMS-sponsored OAI this study will provide unique information on the role of the MR based T2 relaxation time cartilage biomarker in predicting and monitoring knee osteoarthritis in individuals with risk factors for OA and early OA in relation to healthy controls. The specific aims are: (1) To study the prevalence and grade of cartilage and meniscal lesions using the semi-quantitative whole organ magnetic resonance imaging score (WORMS) in normal individuals (n=100), individuals from the incidence (risk factors) (n=300) and progression (early OA) (n=300) cohorts of the OAI aged 45-70 years, and to analyze the relationship of these scores with T2 parameters (mean, spatial distribution and laminar organization) and assess interrelationships between the 3 groups. (2) To determine if baseline T2 parameters (mean, spatial distribution and laminar organization) will predict longitudinal change in WORMS scores and increase in WOMAC (Western Ontario and McMasters) and KOOS (Knee Injury and Osteoarthritis Outcome Score) indices over a period of 2 and 4 years. (3) To assess the longitudinal change in (i) T2 parameters (mean, spatial distribution and laminar organization) and (ii) cartilage and meniscal lesion progression in relation to changes of pain and function scales (WOMAC, KOOS), physical activity (PASE) and physical performance over a period of 2 and 4 years. MR imaging studies will be analyzed semi-quantitatively (WORMS) and quantitatively (T2 relaxation time) at baseline, after 2 and 4 years. Clinical information will be available in all these individuals (WOMAC scores, KOOS, PASE) as well as knee function tests (e.g. 400-meter walk, flexion, extension strength through isometric strength testing). We strongly believe, that the advances in knowledge that we gain through this study will help us better understand the role of T2 values in relation to evolution and pathophysiology of OA. Comparing our findings in the incidence and normal cohorts, it may provide evidence how risk factors impact knee joint health. This study may also provide evidence on how to prevent development of early OA and reduce the devastating economic cost induced by disability and pain associated with OA.